defense secretary chuck hagel has warned russia the u.s. is keeping a sharp eye on the moves. the concern is that president putin could be planning some sort of a power grab. chief national security correspondent jim sciutto joins us. despite these exercises, troops mobilizing on the border, the obama administration seems confident russia will not be moving troops into ukraine? >> reporter: that's the pentagon's assessment they're not going to act. what's changed in the last 24 hours, because the russians have moved these troops, mobilized these war planes, put them on alert as well, if president putin decided he did want to go in they could poomove so quick u.s. would not have a chance to react to it. that's increased the level of nervousness among administration officials. what would the u.s. do in reaction? we're talking really about only diplomatic means, protests, et cetera. because the supreme nato commander and american general breedlove says europe is not planning certainly any military reaction if the russians were to go in. >> it would be a huge deal if they went in